A bandgap or base-emitter voltage is often used as a reference voltage for temperature sensor circuits, over-temperature detection, temperature independent current generation, and the like. For example, a bandgap or base-emitter based current generator (such as a proportional-to-absolute-temperature (PTAT) current generator) may be converted to a voltage generator, where the output voltage is representative of the ambient temperature, for example. Such an arrangement may be applied as a temperature sensor with an analog voltage output.
When using such a temperature sensor in various applications, it is generally desirable to fit the output voltage of the temperature sensor to a desired slope. For example, it may be desirable for the output of the temperature sensor to have a particular voltage corresponding to the lowest temperature of the range of interest and for the output to have another voltage corresponding to the highest temperature of the range of interest. Additionally or alternatively, it may be desirable for the output voltage to conform to a particular slope of voltage per increment of temperature measured, or the like. Generally, a shifting circuit is designed to fit the output voltage to the desired slope, and is implemented with the temperature sensor circuitry.
However, in many cases, the desired slope is not independent of the analog output voltage at a given temperature point. Instead, the temperature slope is proportional to the voltage value at a temperature point. Consequently, the supply voltage of the circuit may need to increase as the temperature slope increases, increasing the needed supply headroom of the circuit. Additionally, the use of the shifting circuit along with a dedicated reference voltage increases the circuit area and complexity of the temperature sensor.
Further, additional errors may be introduced when the temperature sensor is implemented in CMOS technology. Generally, with CMOS technology, the PTAT current is generated from the ground line, so a current mirror is used to redirect the generated current from the supply to the ground, and a resistance is used to convert the current to a voltage. These additional conversion steps have a potential to introduce additional errors to the accuracy of the sensor output.